A radio-frequency (RF) switch is a device that controls the flow of an RF signal, or it may be a device that controls a component or device in an RF circuit or system in which an RF signal is conveyed. As is contemplated herein, an RF signal is one which encompasses low and high RF frequencies over the entire spectrum of the electromagnetic waves, from a few Hertz to microwave and millimeter-wave frequencies. A micro-electromechanical system (MEMS) is a device or system fabricated using semiconductor integrated circuit (IC) fabrication technology. A MEMS switch is such a device that controls the flow of an RF signal. MEMS devices are small in size, being fabricated using IC fabrication methods. A MEMS switch features significant advantages in that its small size translates into a high electrical performance, since stray capacitance and inductance are virtually eliminated in such an electrically small structure as measured in wavelengths. In addition, a MEMS switch also is potentially low-cost due to the IC manufacturing process employed in its fabrication.
MEMS switches are termed electrostatic MEMS switches if they are actuated or controlled using electrostatic force which turns such switches on and off. Electrostatic MEMS switches are advantageous due to low power-consumption because they can be actuated using electrostatic force induced by the application of a voltage with virtually no current. This advantage is of paramount importance for portable systems, which are operated by small batteries with very limited stored energy. Such portable systems might include hand-held cellular phones and laptop personal computers, for which power-consumption is recognized as a significant operating limitation.
Even for systems that have a sufficient AC or DC power supply such as those operating in a building with AC power outlets or in a car with a large DC battery and a generator, low power-consumption is still a desirable feature because power dissipation creates heat which can be a problem in a circuit loaded with many IC's.
However, a major disadvantage exists in prior art MEMS switches, which require a large voltage to actuate the MEMS switch. Such a voltage is typically termed a "pulldown" voltage, and, in the prior art may be anywhere from 20 to 40 volts in magnitude and therefore not compatible with modem portable communications systems, which typically operate at 3 volts or less.
To explain further, the typical MEMS switch uses electrostatic force to cause mechanical movement that results in electrically bridging a gap between two contacts such as in the bending of a cantilever. In general this gap is relatively large in order to achieve a large impedance during the "off" state of the MEMS switch. Consequently, the aforementioned large pulldown voltage of anywhere from 20 to 40 volts is usually required in these designs to electrically bridge the large gap.
Also, a typical MEMS switch has a useful life of approximately 10.sup.6 to 10.sup.8 cycles due to fatigue. Thus, in addition to the above concerns, there is an interest in increasing he fatigue life of such MEMS switches.
Thus there is a need for an electrostatic MEMS switch that is actuated by a low pulldown or actuating voltage and low power consumption with increased cycle life.